1. Field of the Invention
The invention in general relates to side looking sonar equipment, and more particularly, to an arrangement for eliminating gaps in the coverage of a target area.
2. Background Information
In side looking sonar systems, the sonar apparatus is mounted on a carrier vehicle which travels along a course line, or track, at a certain altitude above a target area to be examined. A transmitting transducer propagates acoustic energy to either side of the vehicle and the acoustic energy impinges upon the target area in a relatively narrow strip, such impingement process being known as insonification. A receiver transducer in conjunction with signal processing apparatus forms a relatively narrow receiver beam which receives the acoustic energy reflected from the insonified strip. During the course of travel of the carrier vehicle, multiple transmissions take place and the return signals are processed and portrayed on a line-by-line basis that is a pattern of highlights and shadows analogous to an optically viewed panorama illuminated by side lighting, with objects outlined in such a way as to permit their identification.
Side looking sonar systems, have a coverage gap directly beneath the carrier vehicle and to fill in the gap an angle look sonar system has been proposed, using side looking sonar principles, to project and receive acoustic returns from an area ahead of the vehicle in the gap region. Accordingly, with a combination of the side looking and angle look sonar systems, complete coverage of the target area may be obtained. If however, the carrier vehicle is subject to a cross current during the course of travel, it assumes a certain crab angle resulting in less than complete coverage. The apparatus of the present invention is operable with a system such as described and provides and arrangement whereby complete coverage may be obtained even in the presence of crab angle motion.